Fluorescent pigment accumulation in retinal pigment epithelium of antioxidant-deficient rats

A yellow autofluorescent pigment, generally thought to be indicative of membrane autoxidation, was found to accumulate in the retinal pigment epithelium (RPE) of rats maintained for 32 weeks on diets producing physiological antioxidant deficiency. The largest build-up of fluorescent pigment occurred in rats fed a diet high in polyunsaturated fatty acids (PUFAs) and deficient in alpha-tocopherol (vitamin E), selenium, sulfur-containing amino acids, and chromium. These latter four nutrients have all been implicated in maintaining the antioxidant status of tissues, whereas PUFAs are pro-oxidants. Dietary supplementation with methionine and chromium significantly reduced the amount of fluorescent pigment accumulated in the RPE. Supplementation with all four nutrients further reduced the amount of fluorescent pigment to a very low level. Rats maintained on a normal laboratory diet, relatively low in PUFAs and presumably adequate in other nutrients, accumulated relatively small amounts of fluorescent pigment in the RPE. Of all tissues in the retina and choroid, the autofluorescent pigment was found to be almost entirely restricted to the RPE. The autofluorescence produced in the RPE by antioxidant deficiency was more concentrated than that produced in the testes, kidney, intestine, and heart. This suggests that the RPE is particularly sensitive to physiological antioxidant deficiencies. The increased fluorescent pigment build-up in the RPE of antioxidant-deficient rats appears to correlate with a decreased RPE melanin content. Similar changes in pigmentation have been reported to occur in human RPE with age and in dominantly inherited retinitis pigmentosa. Thus, with respect to its effect on RPE pigmentation, antioxidant deficiency appears to mimic aging and possibly some aspects of one type of retinitis pigmentosa.